Nutrition is defined
as the science of food and its relationship to health. Food is composed
of a wide distribution of nutrients, which have very specific metabolic
effects on the human body. Some of these nutrients are considered to be
essential while others are considered to be non-essential.

Essential nutrients are nutrients that cannot be synthesized by the human
body and therefore must be derived from food sources. Essential nutrients
include vitamins, minerals, amino acids, fatty acids and some carbohydrates
as a source of energy. Non-essential nutrients are nutrients which the
body has the ability to synthesis from other compounds, as well as, from
food sources. Nutrients are generally divided into 2 categories, macronutrients,
and micronutrients (Merck Manual 2).

Macronutrients constitute the majority of an individual’s diet,
“thereby supplying energy, and the essential nutrients that are
needed for growth, maintenance, and activity” (2). Macronutrients
include carbohydrates, proteins, fats, macro minerals, and water. Carbohydrates,
proteins, and fats are interchangeable as sources of energy, with fats
yielding 9 calories per gram, and protein and carbohydrates each yielding
4 calories per gram. For more information on carbohydrates, protein, fats,
macro minerals and water please refer to Nutrition Part II Carbohydrates,
Nutrition Part III Protein, Nutrition Part IV Fats, Nutrition Part V Macro
Minerals and Nutrition Part VI Water.

Micronutrients are vitamins and trace minerals. Vitamins and trace minerals
are labeled as micronutrients because the body only requires them in very
small amounts. Vitamins are organic substances that we ingest with our
foods, and that “act as catalysts, substances that help to trigger
other reactions in the body” (Schwarzenegger 674). Trace minerals
are inorganic substances that once ingested play a role in a “variety
of metabolic processes, and contribute to the synthesis of such elements
as glycogen, protein, and fats” (675). For more information on vitamins
and trace minerals please refer to Nutrition Part VI Vitamins, and Nutrition
Part VII Trace Minerals.